Stokes vector receivers have attracted attention for their ability to enhance spectral efficiency due to the increase in the number of dimensions compared to conventional intensity-modulation and direct-detection (IM-DD) systems. One of the technical advantages of the Stokes receiver is that the original state-of-polarization (SOP) of a transmitted signal can be retrieved with digital signal processing (DSP) even if it is fluctuated during fiber transmission. In this paper, we review DSP technologies for SOP recovery, focusing on the modified constant modulus algorithm (CMA), and the radius directed equalization (RDE) algorithm in the Stokes space. Using computer simulations, we show that these algorithms can track random SOP fluctuations without any penalties.

A novel method and its system design for controlling user's traffic in broadband access segments to enhance fairness
among users are proposed and demonstrated. Recently, various new applications such as consumer generated media (e.g.
YouTube) and peer-to-peer file sharing have been emerging in addition to the conventional applications such as E-mail
and World Wide Web. Such novel applications have behaviors different from those of conventional applications in terms
of traffic burstiness, and they tend to exhaust bandwidth for a certain period of time. Hence, there is a potential risk that
the traffic of small numbers of specific users assumes bad influence on the traffic quality as well as on the experiences of
other users. Such situation must be avoided from the standpoint of service fairness among the users. The proposed
bandwidth control system utilizes QoS-related functions of existing heterogeneous access equipments, and provides a
mechanism for maintaining bandwidth assignment based on each user's profile and history of usage. Control of the user
traffic according to a bandwidth assignment policy is successfully demonstrated using a prototype system implemented
in a testbed.

In next generation networks (NGN) architecture which is standardized in ITU-T, Ri interface is defined as the interdomain
QoS control interface between Resource Admission and Control Function (RACF). By the coordination of NGN
operators using Ri interface, it is expected that more users can obtain high quality network services. However, neither the
design of functional architecture for inter-domain QoS control of RACF nor the control sequence of Ri interface are
provided so far. In this paper, a session-based resource management capability for inter-domain QoS control is
demonstrated for the first time. For a video-on-demand application, the extended RACF is applied and the resource
reservation over different NGN-domains is successfully conducted.

Optical 3R regeneration is of great interest due to its ability to enhance the system margins in photonic network, because it enables to reset transmission impairments induced by channel interaction distortion, accumulation of amplified spontaneous emission (ASE) noise, chromatic dispersion and non-linearities of optical fibers and so forth. In comparison to electrical 3R regenerators, optical 3R regenerators are expected to be less complex and require less high-speed electronic components owing to simple optical signal processing, leading to small footprint, low power consumption and low cost. In this paper, we describe an optical 3R regenerator operable with carrier-suppressed return-to-zero (CS-RZ) modulation format which will be employed in dense WDM (DWDM) network to increase the efficiency of bandwidth utilization. We have demonstrated 3R regenerative transmission using 100 GHz-spacing 40 Gbit/s 5 WDM CS-RZ signals so as to confirm that a DWDM filtering effect can be drastically mitigated by the 3R regenerator.

GMPLS-controlled photonic network utilizing optical cross-connect in conjunction with WDM equipment will soon be realized in core network to partly eliminate OEO terminations in cut-through traffic. In the next step, all photonic end-to-end connection/switching is emerging technology for realizing higher bit-rate transmission with finer datum granularity, and reducing both size and power consumption of network nodes to establish truly transparent and flexible network. In this presentation, all optical signal processing devices as wavelength converters and regenerators for such future all photonic networks will be reviewed.

All-optical wavelength conversion is one of the key technologies in future wavelength division multiplexed (WDM) transparent photonic network. An electro-absorption modulator (EAM) is one of promising candidates for optical nonlinear element to realize optical wavelength conversion due that it has fast absorption recovery in comparison to slow gain recovery of a semiconductor optical amplifier while it has moderate conversion efficiency in comparison to silica fibers or electro-optic dielectric materials. In this paper, cross-absorption modulation (XAM) and cross-phase modulation (XPM) characteristics as well as absorption recovery time of EAM having multiple quantum well (MQW) absorption layer was quantitatively analyzed. Absorption recovery time less than 10 ps were achieved for the MQW EAM due to fast sweep-out of photogenerated carriers by the external electric field. The phase shift induced by 1.5 pJ pulse injection was about 0.2. All-optical 2R type wavelength converter using the MQW EAM in conjunction with delayed-interferometer was tested at bit-rate of 100 Gbit/s. Error-free conversion was successfully confirmed. The operable wavelength bandwidth was investigated at 40 Gbit/s. The bandwidth of 30 nm covering almost full C-band was confirmed. An electro-optical 3R type wavelength converter utilizing rf-driven EAM was also proposed and demonstrated. The intentionally added timing jitter onto the input signal was reduced with simultaneous contrast ratio improvement after the 3R wavelength conversion due to periodical gate closing by the rf-clock drive. These results show that EAM is suitable for optical wavelength conversion at bit-rate range of 40-100 Gbit/s with a reasonable conversion efficiency.

All optical regenerations or wavelength conversions using SOA-based polarization discriminated switch injected by a transparent assist light are reviewed. First, the reduction of a gain recovery time in SOA by injection of a transparent assist light wass discussed. A simple measurement technique of cross gain modulation (XGM) and cross phase modulation (XPM) in SOA was shown to confirm that the injection of transparent cw assist light reduced a gain recovery time without significant reduction in the amount of XGM and XPM. All optical regeneration operation 40Gbit/s as well as bit-rate tunable operation from 10Gbit/s to 80Gbit/s were presented. Simultaneous demultiplexing from 80Gbit/s to 2 channels of 40Gbit/s signals with little loss was also demonstrated. Finally, tolerance to amplitude noise and timing jitter was discussed. Those results indicate that the SOA-based polarization discriminated switch is a promising candidate for all-optical regenerator from the practical point of view.

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